We have had some instances where our emails go to users' junk/spam folders. Please check if there is an activation email from us in there.
Our account activation links time out after one hour. If you click through the activation link when the link has timed out you will land on a page that says "Invalid Signature". If this happens to you, you can send yourself a new link by going back to the login page and clicking the "Activation Link" text.
Then enter your registered email address.
If you continue to have any trouble please submit a request, or contact firstname.lastname@example.org.